WO 2014/044 706 discloses a reactor for the release of hydrogen gas, in other words for dehydrogenation, from a liquid hydrogen carrier medium serving as starting material. The flow of the starting material in the reactor, in particular when flowing through a catalyst packing, results in a pressure loss and flow dead zones. The flow of the starting material in the reactor is hardly influencable. A heating of the catalyst is possible only from below. The heat input into the reaction medium, i.e. the starting material, is impaired. The reaction volume is reduced. The catalyst is ineffective.